The invention relates to a weatherable, plasticizer-free, uncrosslinked, and deep-drawable sheet, especially for use in the internal and external outfitting of automotive vehicles, based on ethylene-propylene-diene terpolymers, homo- and/or copolymers of propylene, and optionally fillers and customary additives, produced by extrusion or calendering, with a sheet thickness of about 0.2-3 mm, as well as to a process for the production of such sheets.
Up to this time, plasticized PVC sheets have been employed for the internal paneling and outfitting of automotive vehicles, such as, for example, side paneling, crash pads, dashboards, headrests, domes, or on external surfaces as corrosion protection. Plasticized PVC sheets exhibit the drawback, however, that the plasticizer during the course of time bleeds out or evaporates and leaves undesirable deposits, for example on the windshields which must be repeatedly removed. Another disadvantage resides in the polyvinyl chloride content since when mounting the sheet in the region of the exhaust duct and of the engine there is the danger of formation of hydrogen chloride, promoting corrosion, on account of the high exhaust gas temperatures. Also, the sheet becomes brittle on account of loss of plasticizer, occurring during the course of time, which has an adverse effect on the functional efficacy and lifetime of the sheet, particularly at temperatures below zero degrees C.
DOS 2,806,726 describes a protective layer for floors of automotive vehicles, designed as drumming insulation, which layer contains a carrier layer on the basis of polyolefins, especially ethylene-propylene elastomer, and at least 30% by weight, preferably at least 70% by weight of fillers based on bitumen, plasticizing materials, such as oils, and acoustically effective mineral substances, such as talc, ground shale, graphite, mica. This heavy sheet, which is predominantly soft-plastic and provides noise protection, is permanently bonded to the sheet metal of the car body by means of vulcanizing adhesives or heat-sealing adhesives. The high filler proportions of this sheet, however, reduce the strength properties of the sheet and, in case of calendered sheets, promote so-called crazing. Since the sheets are shaped during application onto the body parts, crazing is undesirable in any event for optical reasons. Also protection against stone impact is inadequate in this protective layer.
DOS 2,732,969 discloses blends of uncrosslinked ethylene-propylene sequential polymers with isotactic polypropylene which can be processed, for example, by pressure molding or extrusion, into molded articles, such as bumpers, seat shells, moldings, dashboards, spoilers, instrument boards, steering wheel casings, as well as ski boots. These blends, however, depending on their composition, either do not exhibit adequate cold flexibility or do not have sufficient deflection temperature under load.
DOS 2,742,910 describes a thermoplastic elastomer mixture of 25-85% by weight of a practically amorphous ethylene-propylene copolymer and 15-75% by weight of a crystalline block copolymer of propylene, especially well suited for the manufacture of cable sheathing and bumpers for automotive vehicles. However, as stated in DOS 2,821,342, the thermoplastic elastomer mixtures of DOS 2,742,910 are definitely in need of improvement with respect to hardness, tensile strength, increase in high-temperature stability, in connection with a number of usages, and they are surpassed in these properties, for example, by a molding composition and molded parts produced therefrom as set forth in DOS 2,821,342.
DOS 2,821,342 relates to thermoplastic elastomer mixtures containing 30-75 parts of a crystalline, isotactic propylene homopolymer and 25-70 parts of an essentially amorphous, rubbery ethylene-propylene polymer and maximally 15 parts of polyethylene, replacing in proportion the propylene homopolymer. Although these mixtures exhibit, in part, improved properties as compared with binary molding compositions, it has been found that there is definitely a need for improvement in mechanical properties for extreme stresses as concerns the elastomer mixtures known from DOS 2,821,342, in particular regarding the notch impact resistance, tensile strength, and cold flexibility. This is also due, in particular, to the essentially amorphous, rubbery ethylene-propylene polymers utilized On the other hand, higher-crystalline EPDM or EPM elastomers, which can be designated as being partially crystalline, with a crystallization temperature (DSC maximum temperature) from/above 24.degree. C., are considered unsuitable for the areas of usage indicated in DOS's 2,742,910 and 2,821,342.
The company newsletter "Der Lichtbogen" [The Electric Arc]by CHW Huels, September 1974, No. 174, pages 18-22, discloses the use of ethylenepropylene elastomer for injection-molded parts for use in the automobile producing industry as well as for roofing sheets and other products.